There are many types of known electronically actuated fuel injectors that could benefit from the present invention. For instance, one such injector might be a Caterpillar hydraulically-actuated electronically-controlled fuel injector system (see e.g. U.S. Pat. No. 5,121,730), which has an electronically actuated valve that opens to permit flow of high pressure actuation fluid into the injector to initiate injection. When deactivated, the valve is biased to close in order to end injection. The valve acts as a switch to start and stop fuel injection at precise times during an engine cycle. Those skilled in the art will appreciate that the valve's motion must be both fast and complete (fully opened) to produce desired injection characteristics. This type of injection system is time based, meaning that the amount of fuel injected is a function of the amount of time that the valve is opened. In general, injection duration increases with an increase in valve activation duration; however, most valves have a zone of operation in which an increase in valve activation duration actually causes a decrease in the amount of fuel injected. This phenomenon is believed due to the valve member, be it a spool valve or a popper valve, bouncing off its stop because the valve is commanded to close before the valve has reached its fully opened position. In other words, the valve is commanded to close before the valve member has reached its fully open position but its opening momentum causes the valve member to bounce off its stop and close more quickly than it otherwise would under the action of its return spring. Hereinafter, the term "transition zone" will be used to refer to that zone of operation of the injector system in which the electronically actuated valve exhibits the bouncing phenomenon.
At higher injection flows, the spool or popper valve member is pushed and held against its stop during a relatively long injection duration. In some instances when fuel demand is low, such as in low load or low rpm conditions, the valve member bouncing phenomenon can cause the engine to behave somewhat erratically. This erratic behavior is believed due to the fact that, in the transition zone of operation, an increase in valve activation duration causes a decrease in the amount of fuel injected. The valve member bouncing phenomenon causes the valve to close prematurely in a non-linear manner that is very difficult to predict. There is no known prior art that recognizes this problem or proposes a solution thereto.
The present invention is directed to providing a method of staging activation pulses to the injector in a way that avoids the problems created by the valve member bouncing phenomenon.